allow cabal.project to specify/override additional pkg-config depends

[cartazio]

so i'm trying to use the rounded package on recent ghc, and ignoring other challenges, I need to make it aware of a gmp install, because recent ghc dont provide a gmp!

packages: *.cabal

allow-newer: rounded:base,rounded:ghc-prim,long-double:base

package rounded 
    pkgconfig-depends: mpfr, gmp 

is what i'm trying to do, but it looks like that field isn't understood by cabal.project?